The increasing demand for high performance, lightweight, small size portable electronic devices is also increasing the requirements of rechargeable battery performance. Therefore, the amount of energy stored in a battery is increasing. Packing more energy into a cell, however, increases safety concerns. With larger batteries, an increased amount of stored energy is present, resulting in greater hazards, such as a risk that the battery may explode, causing harm to users. Therefore, there is an increasing interest in multiple paths for monitoring the status of a battery or group of batteries during different stages such as, for example, a charging phase, an operational phase, and during and transportation of the battery or batteries. Safety issues have already reached the critical stage in the case of larger batteries used in portable electronics such as laptop computers. It is therefore believed that in the future, these issues will only become increasingly of paramount importance.
Batteries with much larger capacities and increased energy densities are expected to play a significant role in tomorrow's energy and transportation systems. From storing distributed electrical power produced using intermittent renewable resources, to plug-in hybrids cars, all-electrical or battery-fuel cells hybrid cars, extra-large batteries with a large amount of packed energy densely will likely be developed for widespread use.
For instance, one favored type of high-energy density batteries whose use is expanding is the rechargeable lithium-based battery. This type of battery requires precise monitoring during its charging, operational and transportation phases, because if something goes wrong during these stages, the potential for dangerous “venting with flame’ (explosion) could occur. Under certain conditions, such as when a battery is overcharged, overheated or a short-circuit occurs, the chemical reaction can spin out of control, causing a thermal runaway situation and pressure build-up within the cell that ultimately could cause the battery to explode. Therefore, key safety challenges include preventing accidental overcharging, overheating, over-pressure, overshock and damage that could cause an internal short-circuit. Despite various and complex safety mechanisms developed, the safety issue of such batteries remains an important issue in the continued development of batteries such as those utilized in laptop computers and hybrid vehicles.